1. Field of the Invention
The present invention relates to a computer system, and more particularly, to an error sensing and correction apparatus within said computer system for automatically sensing the existence of an error in data stored within said computer system, for correcting the erroneous data, and for ensuring that the error will never be reproduced.
2. Description of the Prior Art
A memory often includes a plurality of integrated circuit chips. The integrated circuit chips each include a plurality of cells. If one or more cells of an integrated circuit chip in the memory fail, the binary data, stored in the cells, is erroneously changed. When the data is read from the memory, the erroneous binary data is included as part of the data read from memory.
Various schemes have been devised to detect the existence of the erroneous data, to correct the data, and to take steps to ensure that the corrected data will be retrieved from memory when the memory is subsequently addressed. For example, application Ser. No. 531,793, filed Sept. 13, 1983, now U.S. Pat. No. 4,608,687 entitled Bit Steering Apparatus and Method for Correcting Errors in Stored Data, Storing the Address of the Corrected Data and Using the Address to Maintain a Correct Data Condition, discloses such a scheme. In addition, application Ser. No. 528,769, filed Sept. 2, 1983, entitled "Memory Correction Scheme Using Spare Arrays" also discloses such a scheme. The above applications are assigned to the same assignee as that of the present invention. In both of the above referenced applications, when erroneous data, withdrawn from a memory unit, is detected, the identity of at least one bit of the erroneous data is determined and, when the erroneous bit is corrected, the identity of the corrected bit is stored in a special store and the corrected bit is stored in a spare unit in the memory unit. In the former above referenced application, the special store is a component located off the memory unit while, in the latter above referenced application, the special store is a component located within the memory unit. In both applications, however, the one bit of the corrected data is stored in a spare unit in the memory unit. A multiple number of spare units are available within the memory unit for this purpose.
As the technology associated with computing systems advances, the failure rates associated with the data withdrawn from the memory unit of the computing systems decrease. As these failure rates decrease, the need for the multiple number of spare units within the memory unit also decreases. However, since some failures will always occur, although the failure rates are low, the need for a spare unit, for the storage of corrected data, still exists.